Iversen, Tommy

Abstract [en]

CP/MAS C-13 NMR spectroscopy was used in combination with spectral fitting to examine the surface structure of hydrated cellulose I fibrils from Halocynthia and Gluconoacetobacter xylinus. To increase the spectral intensities and minimize signal overlap, G. xylinus celluloses site-specifically enriched in C-13 either on C4 or on both C1 and C6 were examined. The experimental data showed multiple C4 and C6 signals for the water accessible fibril surfaces in the highly crystalline celluloses. These signal multiplicities were attributed to structural features in the surface layers induced by the fibril interior, and could not be extracted by spectral fitting in celluloses with a lower degree of crystallinity such as cellulose from cotton.

Malm, Erik

KTH, School of Biotechnology (BIO), Glycoscience.

2014 (English)Doctoral thesis, comprehensive summary (Other academic)

Abstract [en]

Glucans are polysaccharides integral to many materials and biological functions. Under the umbrella of Biomime, the Swedish Center for Biomimetic Fiber Engineering, this work has aimed to improve basic understanding of the biosynthesis of such glucans. This has been achieved through direct investigation of cellulose structure, and by developing the tools to analyze glucan biosynthesis. Notably we have identified a novel chemical effector of glucan synthesis processes and developed a proteomic toolkit useful for analyzing membrane-bound glycosyltransferases, the enzyme group responsible for glucan biosynthesis. During this work, glucan synthesis has been studied using both Gluconacetobacter and Populus cell suspension cultures.

Publication I.Gluconacetobacter cellulose (BC) was used as a base to create a novel and well characterized nano-material with improved mechanical properties. This novel composite of BC and hydroxyethylcellulose (HEC) had improved tensile strength compared to pure BC. Through thorough study utilizing dispersion measurements, electron microscopy, nuclear magnetic resonance and X-ray diffraction it was shown that the improved properties derived from a layer of HEC coating each fibril.

Publication II. Bacterial cellulose was labeled in specific positions with 13C (C4 and C6). These samples were analyzed by CP/MAS NMR along with cellulose samples from cotton and Halocynthia sp. For each sample spectral fitting was performed and general properties of crystal allomorph composition and fibril widths were determined. Calculations were also made for water accessible surfaces of the fibrils. The results showed that water accessible C4 surface signals are reflective of the allomorph composition of the sample, along with a distorted signal that derives due to fibril imperfections. Water accessible surface signals from the C6 region are instead derived from rotamer conformations of the C6 hydroxymethyl groupsfrom glucose residues.

In Publication III, a high-throughput screen was used to identify an inhibitor of Golgi-derived glycosyltransferase activity, termed chemical A. The structural basis for inhibition was determined and in vitro assays of callose synthesis were performed. The in vitro assays revealed chemical A to also be an activator of callose synthesis. To understand this activation kinetic studies were performed, showing that chemical A is a mixed type of activator, which can bind either the free enzyme or the enzyme-substrate complex. Chemical A has uses in chemical genetics for dissecting processes involving callose synthesis, such as stress response and cell-plate formation.

In publication IV, we present an in-house developed platform for proteomics with a distributed processing model. This in-house system has been central to many proteomics tasks, including for those presented in publication V, and is being distributed as the Automated Proteomics Pipeline (APP).

In publication V, conditions for enrichment of Detergent-Resistant Microdomains (DRM) have been optimized for Populus trichocarpa cell cultures. The proteins enriched in DRM were identified using mass spectrometry based proteomics, and a functional model for DRM was proposed. This model involves proteins specialized in stress response, including callose synthase, and cell signaling. This further strengthens the arguments for DRMs as sites of specific cellular functions and confirms they play a role in glucan synthesis.